This invention relates to a filler unit for adding replenishment liquid to a container to a predetermined, desired level. In one application, the unit is suitable for use in adding replenishment water to the electrolyte contained in a secondary battery.
Secondary battery cells have, traditionally, been provided with replenishment water to make up for water lost from the electrolyte due to evaporation and electrolysis. The process of adding water is simple when the number of battery cells is small and the batteries are readily accessible. For example, in the case of automobile batteries, battery cells Can be inspected and filled manually.
With larger batteries, the number of battery cells is often so large and the accessibility so poor that the task of replenishing by hand can become particularly difficult and time consuming.
Various filling systems have been developed which provide requisite water to all the battery cells via a single supply line. These have proved either insufficiently robust or prone to a variety of technical deficiencies which have been known to result occasionally in battery cells being overfilled, and in some cases not being filled at all.
In some filler units there are level sensors including floats that are in direct contact with the electrolyte, the floats being connected to valves. When the electrolyte level rises sufficiently the valves close and stop the flow of water. A variety of aggressive substances are released by the battery elements in normal operation which have a deleterious effect on contact with the floats, resulting in the floats remaining fixed in position, and therefore not able to control the flow of water into the battery cells.
Other designs, mindful of this disadvantage, utilize the water supply pressure itself as a shut-off mechanism. The flow rete is necessarily fast in order to set up the required degree of suction inside a specially shaped control duct. When the electrolyte level rises to cover the lower end of this duct, a resulting air pressure change inside the control duct triggers an internal protected control mechanism shut. Partial exhaustion of the water supply pressure results in the control mechanism not receiving an adequate trigger signal when the required level is reached, and thus the flow of water into the affected battery cells will not be stopped.
In yet another type of filter an air pressure sensing tube reaches into the battery cell. As the electrolyte level rises against the open bottom end of this tube, the tube becomes sealed, and the air pressure inside the tube rises, thereby providing a back pressure against inflowing water entering the battery cell from a special vessel housed above the cell. The water level inside this vessel is controlled, and when a condition of pressure equilibrium is reached along the flow path of the water from the vessel into the battery cell the flow of water into the cell is stopped. Such a filler is disclosed in International published patent application W098/40653.
Some air pressure sensing filler devices rely on control of the water level in the vessel by means of a feed and overflow arrangement whereby the inflow is greater into the vessel than the inflow into the cell, and consequently there is an excess which flows out of the overflow. Others rely on a float and shut-off valve housed within the vessel, whereby the position of the float and consequently the degree of opening of the valve provides an inflow into the vessel which exactly matches the inflow into the cell.
An advantage of air pressure sensing filler devices is their simplicity. There are no sensitive parts in contact with the surface of the electrolyte.
Furthermore, they are not affected by supply underpressure, while a feature can be included which can protect against supply overpressure.
Since it is the inflowing replenishment water which provides the air seal at the head of the air pressure level sensing tube, the seal is preferably formed before the electrolyte level has closed off the bottom opening of the level sensing tube Consequently in some types of air pressure sensing filter devices, such as that disclosed in W098/40653, if the seal is formed with the bottom opening of the tube already closed by the electrolyte, additional water can flow into the cell, causing the electrolyte level to be raised to a higher level than the desired level.
According to the first aspect of the invention there is provided a filter unit for dispensing a liquid into a container to top up the container to a predetermined desired level, the unit including a vessel for containing the liquid to be dispensed, means for establishing a first predetermined substantially constant head of liquid in the vessel, means defining at least one flow passage communicating between the vessel and the container, the flow passage defining means including a downpipe extending downwardly into the container, means for establishing a second head of liquid within the container responsive to the first head, the first and second head establishing means being arranged to co-operate to form there-between a pressurized air column in the downpipe, which is sufficient to prevent the inflow of water from the vessel to the container in response to filling of the vessel whilst the pre-existing level of liquid in the container is equal to or higher than the desired level, and evacuating means for reducing the level of the first head of liquid to a venting level at which the pressurized air column is vented to allow the pressurized air column to re-establish itself an topping up of the vessel, so as to prevent overtopping of the container.
In a preferred form of the invention, the means for establishing the first predetermined head of liquid includes divider means for dividing the vessel into a first vented portion in Which the liquid is permitted to reach a predetermined maximum head-defining level and a second air entrapping portion arranged to entrap the pressurized air column.
Preferably the evacuating means is arranged to evacuate the vessel prior to a subsequent topping up operation to the venting level at which the pressurized air column is depressurized by venting it to atmosphere via the, first vented portion.
Conveniently, the evacuating means is arranged to allow the level of liquid in the vented portion of the vessel to fall below the level of the divider means between topping up operations so that the second air entrapping portion is vented to atmosphere and the pressurized air column is depressurized.
In one form of the invention, the evacuating means comprises at least one aperture defined in a side or base wall of the vessel below the level of the divider means.
In an alternative form of the invention, the evacuating means comprises at least one opening via which the vessel vents to atmosphere, so as to allow evaporation of the liquid in the vessel between topping up operations
Advantageously, the predetermined head-defining level is defined by an overflow rim or weir which is arranged to permit the overflow to follow a flowpath outside the container.
The means for establishing the second predetermined head of liquid preferably includes the downpipe terminating in a mouth portion which extends to a predetermined level a predetermined distance below the desired level, the distance being sufficient to establish the second head of liquid.
The entrapping portion is typically defined by the divider means and includes a first divider which extends downwardly to a first predetermined level within the vessel, and a second divider weir which extends upwardly to a second predetermined level above the first level and which divides the vessel from the downpipe, the difference in height between the first and second levels being sufficient to allow the second head to act and to entrap the pressurized column of air.
Conveniently, a restricted orifice is located at the head of the downpipe downstream of the entrapping portion, the restricted orifice being arranged to supplement the action of the first and second liquid head establishing means in defining an upper boundary of the pressurized air column at which a condition of pressure equilibrium is attained to cause the flow from the vessel to the container to cease automatically.
Advantageously, the means for establishing the first head of liquid in the vessel includes a float chamber having an uppermost inlet conduit and carrying a float valve arranged to shut off the inlet conduit in the event of the liquid in the float chamber reaching a predetermined level.
The filler unit is typically a battery watering unit, in which the container is a battery cell, and in which the downpipe is arranged to extend through a replenishment aperture in the cell, so that the watering unit is mounted atop the cell.
The invention extends to a battery watering unit for dispensing electrolyte into a battery cell to top up the cell to a predetermined desired level, the unit including a vessel for containing the electrolyte to be dispensed, means for establishing a first predetermined substantially constant head of electrolyte, means defining at least one flow passage communicating between the vessel and the cell, the flow passage defining means including a downpipe extending downwardly into a replenishment aperture in the cell, means for establishing a second head of electrolyte within the cell responsive to the first head, the first and second head establishing means being arranged to co-operate to form therebetween a pressurized air column in the downpipe which is sufficient to prevent the inflow of electrolyte from the vessel to the cell in response to filling of the vessel whilst the preexisting level of electrolyte in the cell is equal to or higher than the desired level, and evacuating means for reducing the level of the first head of electrolyte to a venting level at which the pressurized air column is vented to allow the pressurized air column to re-establish itself on topping up of the vessel, so as to prevent overtopping of the battery cell.